There are a wide variety of different types of electric motor applications where the load is cyclic in nature. Examples of cyclic load applications include cams, cranks, pumps, sinusoidal loads, regenerative loads, and the like. While the cyclic loading in such applications also requires larger motors and power transmission elements, it can be particularly demanding on the power source for the motor. When the power source is a generator, the cyclic loading typically causes generator over-speeding and/or stalling as the load changes, tending to reduce the operational life of the generators. When the power source is the electric grid provided by a utility company, the cyclic loading increases the peak demand on the grid.
One of the ways industry compensated for cyclic loading was to use larger power sources in the cyclic load applications. When the power source was a generator, a larger and more expensive generator was used resulting in the need for a larger and more expensive engine. Also, using larger generators and engines is generally not as efficient as using optimally sized generators and engines. As a result, the use of fuel to power the engine increased. When the utility supplied electric grid was used as the power source, the rating of the power lines and transformers was increased with a corresponding increase to the cost of these components. In addition to the increased cost and size of the larger components, many electric power providers are now charging higher rates to customers who have higher peak loads.
Another method to attempt to manage the cyclic variation in load has been to vary the frequency of the alternating current power provided to an induction motor, and thereby control its speed, based on historical data, as the power demands of the cyclic load change throughout its cycle. A significant drawback of this approach is the reliance on historical data about the cyclic load. Such an approach does not react quickly to changing conditions affecting the cyclic load. Further, if the cyclic variation in load is such that the generator or other power source is insufficient to operate the machine through a complete cycle, it is impossible to collect the historical data necessary to calculate the frequency commands required to reduce the variation of the load.